Eco-Friendly Conversion of Waste Zeolite Dust into Dual Oil/Water Affinity Sorbents via HPGR-Based Agglomeration–Deagglomeration

Abstract

This study presents an innovative, eco-friendly approach for converting waste zeolite dust into efficient petroleum sorbents through an integrated agglomeration–deagglomeration process using high-pressure grinding rolls (HPGRs). This method generates secondary porosity without calcination, enhancing sorption while reducing greenhouse gas emissions and supporting sustainable development by valorizing industrial by-products for environmental remediation. The study aimed to assess the influence of binder and water content on petroleum sorption performance, textural properties, and mechanical strength of the produced sorbents, and to identify correlations between these parameters. Sorbents were characterized using mercury porosimetry (MIP), sorption measurements, mechanical resistance tests, scanning electron microscopy (SEM), and digital microscopy. Produced zeolite sorbents (0.5–1 mm) exceeded the 50 wt.% sorption threshold required for oil spill cleanup in Poland, outperforming diatomite sorbents by 15–50% for diesel and 40% for used engine oil. The most effective sample, 3/w/22.5, reached capacities of 0.4 g/g for petrol, 0.8 g/g for diesel, and 0.3 g/g for used oil. The sorption mechanism was governed by physical processes, mainly diffusion of nonpolar molecules into meso- and macropores via van der Waals forces. Sorbents with dominant pores (~4.8 µm) showed ~15% higher efficiency than those with smaller pores (~0.035 µm). The sorbents demonstrated amphiphilic behavior, enabling simultaneous uptake of polar (water) and nonpolar (petrochemical) substances.

1. Introduction

Zeolites are microporous, hydrated aluminosilicates with a crystalline three-dimensional framework composed of SiO₄⁻⁴ and AlO₄⁻⁵ tetrahedra linked by oxygen atoms. Their well-defined pore structure (4.5–7.0 Å), high surface area, and thermal stability, combined with tunable composition, endow them with exceptional ion-exchange and sorption properties [1,2,3]. These unique physicochemical properties have positioned zeolites as essential materials in environmental protection, particularly for removing heavy metals and organic pollutants. As a result, they find extensive applications in wastewater treatment, gas separation, catalysis, and molecular sieving [1,2,3,4]. Importantly, the Si/Al ratio plays a significant role in determining various properties of zeolites, such as their ion-exchange capacity, thermal and hydrothermal stability, the concentration and strength of Brönsted-type acid sites, and the overall activity and selectivity [5]. This interplay between composition and functional performance underscores the versatility of zeolites in addressing environmental challenges.

Given the increasing industrial demand and the strategic importance of zeolites in environmental applications, the rational management and optimal utilization of this valuable natural resource have become essential for ensuring sustainable development. In this context, a major challenge lies in processing natural zeolitic rocks, which generates considerable amounts of fine, highly disperse zeolite dust—a poorly utilized by-product. This dust not only hinders the efficient use of high-value zeolites but also raises environmental concerns due to its contributions to atmospheric pollution. However, transformation of the zeolite dust (by-product) into a valuable material is achievable through agglomeration into larger particles. Compaction of the zeolite powder into shaped pellets (agglomerates) enables its commercial utilization, and supports a more sustainable approach to managing this distinctive resource. Despite this potential, the agglomeration of fine zeolite particles remains a complex process requiring further investigation, as current compaction methods are not yet fully effective [6,7,8].

One of the primary challenges associated with zeolite agglomeration is its high alkalinity, which negatively impacts the performance of many binding agents [9]. Therefore, the careful selection of the specific binder—both in terms of its quality and quantity—is essential. In addition to the use of an appropriate binder that imparts structure to the granules, the granulation technique also plays a critical role. The compaction process may adversely affect the pore size distribution within the secondary porous system, which directly influences the sorption properties of the final product [10]. The distribution of binder and powder particles in the microstructure determines granule quality. The specific microstructure as well as the chemical interaction between binder and powder particles can affect the packing density of the granules in diverse manners such as enhancing the meso- and macroporosity surface or creating the densely packed structure without any pores [11].

Asgar Pour et al. [12] and Bingre et al. [6] conducted comprehensive literature reviews on zeolite powder agglomeration methods. Researchers [1,12] highlighted substantial gaps in the available data regarding zeolite powder granulation, which is often inconsistent, incomplete or even sometimes inaccessible due to patent protection. While zeolite synthesis methods are well-documented [9], agglomeration techniques have received limited academic attention. Michels et al. [13] emphasized that zeolite agglomeration is a neglected area in fundamental zeolite research, and this needs to change particularly in specific applications such as catalysts. Additionally, research on the impact of binders and processing conditions on granulated zeolite properties remains scarce [8].

The predominant method for the industrial-scale agglomeration of natural zeolite powder is wet granulation, typically employing techniques such as pan granulation or extrusion [2,7,14,15]. This process utilizes a wide range of clay binders (e.g., bentonite, attapulgite, and kaolinite) [14,15,16,17]. These clays contain group 1 and 11 elements (e.g., Na, K, Mg, Al, Ca), functioning as mobile non-framework cations that interact, with zeolite via ion exchange, thereby altering the zeolite acidity. Moreover, press compaction promotes cation migration from the clay to the external framework sites of the zeolite influencing zeolitic granule properties such as selectivity toward different substances, catalytic performance, thermal stability, and mechanical resistance [12,13,18].

Importantly, different clay-based binders affect different zeolite types in distinct ways. For example, Na-montmorillonite-based binders combined with mordenite (zeolite) improve physicochemical properties [19], whereas kaolinite-based binders with dealuminated mordenite enhance coke stability but may also reduce catalytic efficiency in methanol-to-gasoline process [20]. Similar trends have been observed for H-gallosilicate zeolites [21]. Moreover, kaolinite promotes the formation of an open-pore structure in zeolites. In contrast, silica or boehmite binders applied in extrusion may adversely affect the catalytic properties of zeolites [12]. Bentonite and attapulgite clay binders enhanced the catalytic properties of the X- and Y-type zeolites [18]. A major limitation of clay-based binders is their sensitivity to water, which can compromise the granules’ mechanical integrity and disrupt the compaction process [22,23,24].

Besides clays, inorganic binders such as silica, alumina, titania, and zirconia, or their combinations, are widely used. Alumina-based binders, in particular, increases acidity through aluminum migration into the zeolite framework and the introduction of sodium cations [25,26].

Organic binders such as cellulose, polyethylene glycol (PEG), and polyvinyl alcohol (PVA) are predominantly used in extrusion due to their low viscosity and lubricating properties, which prevent cracking. Additives like thickeners, wetting agents, plasticizers, and peptizing agents (e.g., nitric or acetic acid) improve binder distribution and mechanical strength of the pellets [2,27,28,29,30,31,32]. In the agglomeration of zeolite powder, not only the type but also the amount of applied binder is contingent upon the desired outcome and the specified requirements regarding the properties of the final product. Usually, binder content in zeolite agglomeration ranges from 10% to 20%, although cases of usage exceeding 50% have also been reported [33]. Generally, higher binder amounts enhance mechanical strength but reduce porosity, adversely affecting adsorption capacity [2,34]. However, binder quantity alone does not solely determine sorption properties. For instance, Charkhi et al. demonstrated that using 20–40% bentonite, combined with an innovative forming method, resulted in improved sorption and maintained mechanical integrity—highlighting that the impact of processing techniques also significantly affects performance [35].

Recently, particular research interest has turned to more advanced and sophisticated zeolite agglomeration methods than wet pan granulation or extrusion, such as binder-free granulation, especially through the implementation of 3D printing for shaping carbon capture zeolite materials and gas separation adsorbents [36,37,38,39,40,41]. While the 3D printing method appears to be an up-and-coming approach for binder-free zeolite granulation, its high costs and energy requirements currently restrict its application primarily to laboratory-scale conditions, with only a few exceptions at the commercial scale [42].

As highlighted in the preceding brief literature review, high-pressure compaction represents an agglomeration method for natural zeolite dust that has not been extensively studied. While some research has investigated this technique, it has mainly concentrated on synthetic zeolites instead of their natural counterparts. For instance, Bazer-Bachi et al. investigated the compression-based shaping of metal–organic frameworks (MOFs) [43], while Panek et al. examined the impact of various compaction techniques—such as tableting, extrusion, and briquetting—combined with different binders like molasses, waterglass, and cement on the textural properties of Na-P1 zeolite [44].

While roll compaction/dry granulation (RCDG) has been a well-established technique in the pharmaceutical industry since its inception in 1965, its applications have recently garnered renewed interest [45,46,47]. Despite the advancements in understanding and optimizing RCDG for pharmaceutical applications, its potential for natural zeolite dust agglomeration remains largely unexplored. Due to the low manufacturing cost, reliable production of the homogeneous granules, enhanced control over operation conditions and possibility of significant reduction in water and binder and/or powder lubricants content in agglomerated mixture, the RCDG surpasses the complex wet granulation process [45,46,48]. Moreover, the great advantage of the RCDG method in comparison to wet granulation is the capability to handle materials susceptible to heat and moisture [47]. The main drawback in roll compaction dry granulation is the bimodal size distribution of the produced agglomerates [49].

In roller compaction (RC), a powder mixture is compressed between two counter-rotating rolls, under a defined specific compaction force (SCF), forming intermediate products known as ribbons. Ribbons are milled into granules of desired size—the final product of the RCDG [47,48]. According to Miller, granule formation in roll compaction dry granulation involves particle rearrangement, deformation, fragmentation, and bonding—each occurring in distinct roll zones (feeding, compaction, and extrusion) associated with different force levels: feeding zone, where particles rearrange under low stress, compaction zone, where intense pressure causes deformation, fragmentation, bonding, and finally, the extrusion zone [50].

In roll compaction–dry granulation (RCDG), the properties of granules are shaped by two main groups of factors: process parameters (compaction force, roll gap width, and roll speed) and formulation-related variables (binder type, dosage, and particle size) [47]. An insufficient binder dosage may result in incomplete surface coverage of the particles, leading to agglomerates with poor mechanical strength and suboptimal size. Conversely, excessive binder content may adversely affect granule performance by hindering disintegration, reducing solubility, inhibiting sorption, and compromising the yield of the desired particle size. In general, in dry granulation plastic binders are preferred due to their ability to enhance interparticle bonding, increase tensile strength, and control granule size [51]. García-Triñanes et al. reported that organic liquid binders (e.g., vinasse, molasse) applied in the roll compaction of caustic magnesia improve both product quality and process efficiency [52]. Regarding binder particle size distribution, smaller particles with a large surface area are preferable in roll compaction agglomeration; however, the optimal size depends on the intended granule application [52]. Yusof et al. demonstrated the possibility of using the roll compaction in maize powder agglomeration [53]. More recently, Lim et al. reported that roll compaction technology constitutes an effective approach for agglomerating problematic powdered radioactive waste, resulting in a substantial reduction in waste volume through the formation of mechanically resistant pellets [54].

In this study, we focused on the roll compaction/dry granulation (RCDG) method, which we propose as a promising technique for the agglomeration of natural zeolite dust.

The main objective of this study was to investigate the influence of varying binder and water dosages on the sorption and performance properties of zeolite sorbents shaped from zeolite powder by-product using roll compaction agglomeration. A comprehensive physicochemical analysis of the feed materials was conducted, including assessments of textural properties (N₂ adsorption/desorption, surface area), particle size distribution, and morphology via SEM, as well as phase composition through X-ray diffraction (XRD).

Subsequently, the sorption capacities of the produced zeolite sorbents for petrochemical compounds (diesel, used engine oil, and petrol) and water were evaluated, along with their mechanical properties (crush resistance). A critical aspect of the research was the characterization of the pore structure through Hg-porosimetry and SEM microstructural observation of the zeolite-based sorbents to elucidate the structure–property relationships.

Moreover, this study clarified the effect of varying binder and water content in the feed material for roll compaction on the textural and mechanical properties of the produced zeolite agglomerates, and evaluated whether different dosages of binder and water affect the sorption efficiency of the sorbents.

To the best of our knowledge, this is the first systematic research of natural zeolite dust agglomeration using this integrated dry granulation approach—agglomeration and deagglomeration within a single high-pressure roller system. The novelty of this work lies not only in demonstrating the technical feasibility of RCDG for zeolite-based materials, but also in offering new insights into how binder and moisture content affect agglomerate quality in pressure-based systems. From an environmental standpoint, a key outcome of this study is the indication that the proposed agglomeration strategy not only contributes to the mitigation of greenhouse gas emissions, but valorizes industrial waste by converting it into a sustainable, value-added material.

Finally, this study addressed a significant research gap by exploring the use of zeolite-based sorbents for petroleum remediation on solid surfaces—an area largely overlooked in favor of aqueous applications. This non-standard new approach expands the conventional use of zeolites beyond liquid-phase systems, offering another direction in environmental remediation.

2. Materials and Methods

2.1. Materials

The natural zeolite dust used in the experimental studies, intended for the production of zeolite-based agglomerates for the petroleum-derived compound sorption, was a by-product of Miocene volcanic tuff processing (clinoptilolite-rich rock) sourced from the Sokyrnytsya deposit (48°30′44″ N, 24°14′45″ E) in Ukraine’s Transcarpathian region.

The binder used for the agglomeration of natural zeolite dust was an inorganic commercial product in solid form, sourced from a local supplier in Poland. Due to a pending patent application, specific details regarding the binder’s manufacturer have been intentionally omitted from this manuscript.

To contextualize the sorption performance of the produced zeolite-based agglomerates, their properties were compared with diatomite-based petroleum sorbent produced via wet pan granulation and energy-intensive calcination, as well as the commercial diatomite-sorbent DAMSORB (Producer Imerys Industry Minerals, Nykobing Mors, Denmark).

2.2. Methods

2.2.1. Chemical and Mineral Analysis

The chemical composition of the natural zeolite dust and binder was analyzed using ED-XRF (Epsilon 3x, Panalytical, Almelo, The Netherlands)

The mineral composition was determined via powder X-ray diffraction (XRD) using X’pert MPD X-ray diffractometer (Panalytical, Almelo, The Netherlands) equipped with a PW 3020 goniometer (Panalytical, Almelo, The Netherlands). Measurements were conducted in the 2θ range of 7–55°, with a step size of 0.0167° and a collection time of 120 s per step, using a 0.5° divergence slit and a 10 mm mask. CuKα radiation was employed at 45 kV and 35 mA. Data analysis was performed using PANalytical HighScore Plus (version 4.9) software with the JCPDS-ICDD database. Samples were ground to <0.100 mm. in an agate mortar and back-loaded into a 27 mm diameter sample holder to minimize preferred orientation effects.

2.2.2. Morphology and Structural Analysis

Morphological and structural characteristics of the raw materials and produced agglomerates were examined using the following instruments:

• Scanning electron microscope (SEM)—Thermo Scientific Quattro ESEM (ThermoFisher Scientific, Waltham, MA, USA )operated in EBSD mode at 20 kV and ~10 mm working distance. Samples were coated with a ~20 nm carbon layer.
• Polarizing microscope (transmitted and reflected polarized light on thin sections).
  Nikon Eclipse LV 100 POL (Nikon GmbH, Essen, Germany)
• Stereoscopic microscope—Nikon SMZ 1000 (Nikon GmbH, Essen, Germany)

2.2.3. Textural Analysis

The textural parameters (specific surface area, volume of micropore and mesopores, and pore distribution) for zeolite dust were determined based on the progression of low-temperature adsorption/desorption isotherms of the nitrogen vapor at a temperature of −194.85 °C using the micrometrics ASAP 2020 (Micromeritics Instrument Corporation, 4356 Communications Dr., Norcross, GA 30093-2901, USA). The sample was degassed (10⁻¹ Pa) at 350 °C for 24 h. The textural characteristics were determined by the Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods. The mesopore volume was determined by using BJH method in the range of mesopore of 2 to 50 nm. The macropore volume (Vmac) was calculated using the following equation:

Vmac = Vtot 0.99 − (Vmic + Vmes BJH)

The average pore diameter (Dp) was determined by the BET results (4V/A by BET), while average pore width (4V/A) was determined by the BJH results (4V/A). The pore size distribution was obtained from BJH sorption data.

The textural parameters for produced zeolite-based agglomerate sorbents were determined by Mercury Intrusion Porosimetry (MIP). MIP tests were performed using PoreMaster 33 Quantachrome Instruments, which operate in the pressure ranges from vacuum to 30,000 psi (200 MPa). Prior to the Hg intrusion porosimetry test, the samples were degassed (10⁻¹ Pa) at 350 °C for 16 h. The pore size distribution (PSD) was determined from the Washurn equation using a surface tension of mercury of 480 N m⁻¹ and the contact angel 140°.

2.2.4. Particle Size Distribution

The particle size distributions of the raw materials (natural zeolite dust, binder) were analyzed using the Malvern Mastersizer 2000 (Malvern Panalytical, Malvern, Worcestershire, UK) in dry mode, following ISO 13320 [55]. On the other hand, for produced zeolite-based agglomerates, grain size distribution was determined by sieve analysis in accordance with EN 933-1 [56].

2.2.5. Basic Bulk Properties

The specific density of the powders was determined using the pycnometric method according to EN 1097-7 [57], while the bulk density and compacted density was determined according to EN 1097-3 [58].

The moisture contents of zeolite dust, agglomeration process feedstock and moldings were determined using a weighing machine by drying at 105 °C to constant weight.

The efficiency of roll compaction granulation was assessed by sieve analysis, focusing on >0.5 mm particles (commercial sorbent standard). A higher fraction yield indicated better agglomeration.

2.2.6. Mechanical Strength Measurement

Mechanical strength was assessed by the gravitational drop test: ~50 g of dried agglomerates (0.5–1 mm and 1–2 mm) was dropped 3× from 1 m onto a steel plate. Post-test mass retained on a sieve (0.250 or 0.500 mm) was used in the following equation:

K = AR/A × 100%

where

A—weight before drop.

AR—weight after sifting.

2.2.7. Sorption Measurements

• Sorption capacity—Westinghouse test

Sorption properties of petrol compounds and water on produced zeolite-based sorbents were determined via the Westinghouse method using a 70 mm × 75 mm stainless steel mesh cone (mesh size 0.250 mm). The sorption of two different petrochemical compounds, diesel oil (Verva On, ORLEN, Poland) with a density 0.833 g/cm³ and used engine oil (purchased from local automotive workshop with a density 0.885 g/cm³), were used as sorbates. A 20 g sample (dried to constant mass) was immersed in these adsorbents for 10 min, drained for 5 min, and weighed.

Absorbency (R) was calculated as follows:

R = (m2o − m1o)/m1o × 100%

where

m1o—weight of dry sample.

m2o—weight of saturated sample.

• Maximum Sorption Capacity—Droplet Experiment

The maximum sorption capacity of petroleum-derived compounds by the produced zeolite-based sorbents was determined using a droplet experiment based on the classical Westinghouse method, adapted from [59]. In this procedure, a 3–4 g portion of dried sorbent was evenly spread in a Petri dish, and the absorbate was applied dropwise until saturation was achieved. The experiment was considered complete when a subsequent drop of absorbate was no longer absorbed and began to overflow. This point was recorded as the sorbent’s maximum sorption capacity. In the experiment, three different petroleum-derived compounds were used as absorbates: diesel oil (Verva ON, Orlen petrol station network, density 0.833 g/cm³), petrol (EuroSuper 95, Orlen petrol station network, density 0.775 g/cm³), and used engine oil (obtained from a local automotive workshop, density 0.885 g/cm³).

Maximum sorption capacity was calculated as follows:

S = (Mp − Mo) × 100%

where

Mp—weight of saturated sample.

Mo—weight of dry sample.

2.2.8. Agglomeration Process of Natural Zeolite Dust

Agglomeration processes of the natural zeolite waste dust were conducted using the roll compaction–dry granulation (RCDG) technique on a laboratory high-pressure grinding roller (HPGR) equipped with smooth-surface forming rings with a roller working diameter of 0.30 m and gravity feed. Figure 1 schematically presents the zeolite dust agglomeration technological process. The proposed agglomeration process follows a two-step approach integrated in one operating system (HPGR) (Figure 1). In the technological system diagram (Figure 1), blue symbols numbered 1–9 depict the specific sequence of actions in the process. To visually complement the process, representative photos of the product at each stage are provided (see Figure 2A,B, Figure 3 and Figure 4A,B).

Firstly, the feed dust (Figure 2A) was agglomerated using rolling mill resulting in ribbon formation (Figure 2B). In the next step, the ribbons (Figure 3) were crushed using the same high-pressure roll compaction equipment, but with minimal roller force (approximately 20 kN) and a roll gap width of 3.5 mm, forming zeolite pellets (agglomerates). The integration of compaction and crushing within a single device significantly enhances process efficiency, eliminating the need for additional equipment and streamlining production. Finaly, the agglomerates were classified by grain size using a vibrating screen to separate two narrow grain classes of 0.5–1.0 mm and 1–2.0 mm (Figure 4). Although the most commercial oil sorbents have a grain size of 0.5–1.0 mm, in this research, the agglomerates with a particle size 1–2.0 mm were also produced and examined in accordance with the research scope outlined in the paper.

Importantly, the developed agglomeration process was conducted in a closed technological system through the roll press, meaning that fractions below 0.5 mm and above 2.5 mm remain within the cycle, indicating that the proposed approach is waste-free.

Various levels of binder (2.5%, 5%, 7.5%, 10%) and water-to-powder feed ratios (20%, 22.5%, 25%) were used in forming the zeolite agglomerates (

Table 1. Composition of feed materials for agglomeration.

Produced Zeolite-Based Agglomerates	Binder [%]	Zeolite Powder [%]	Water [%]
1/w/20	2.5	97.5	20
2/w/20	5.0	95.0
3/w/20	7.5	92.5
4/w/20	10.0	90.0
1/w/22.5	2.5	97.5	22.5
2/w/22.5	5.0	95.0
3/w/22.5	7.5	92.5
4/w/22.5	10.0	90.0
1/w/25	2.5	97.5	25
2/w/25	5.0	95.0
3/w/25	7.5	92.5
4/w/25	10.0	90.0

). The homogenization of powder feed (fine-grained zeolite and binder) was performed in a dynamic counter-rotating granulator, followed by achieving specific moisture levels by adding varying amounts of water, and compaction in HPGR. The roll compaction process was carried out with constant parameters of the roller press: roller speed 0.1 m/s, roller force 150 kN, and roll gap width 3 mm.

To sum up, the conducted experiment confirms the novelty and practical applicability of using a single, integrated HPGR (high-pressure grinding rolls) system for the agglomeration of zeolite powder. This is the first reported use of HPGR technology for the simultaneous agglomeration and deagglomeration of zeolite-based materials. Unlike conventional granulation methods—such as wet pan granulation or extrusion followed by energy-intensive calcination—this approach eliminates the need for additional equipment and thermal treatment. It operates as a closed-loop, waste-free system with internal material recirculation, offering significant environmental and technological advantages.

Overall, these findings highlight the innovative character of the proposed approach and its strong potential as a sustainable and efficient alternative for zeolite agglomeration, clearly distinguishing it from previously developed techniques in this field [45,47,48].

3. Results and Discussion

3.1. Characteristics of Raw Material Prior to Agglomeration Process

3.1.1. Chemical and Mineralogical Composition

Table 2. X-ray fluorescence (XRF) analysis of natural zeolite dust (by-product) for agglomeration.

Oxide Composition [wt.%]
SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	Na2O	K2O	P2O5	TiO2	Mn2O3	SrO	ZnO	LOI
68.76	11.7	1.98	2.58	0.72	0.25	3.28	1.21	0.02	0.16	0.01	0.04	0.01	9.28

presents the chemical composition (XRF analysis) of the zeolite dust, while Figure 5 illustrates its XRD pattern. The XRF and XRD results confirmed that clinoptilolite is the main mineralogical phase present in the investigated zeolite. Other identified mineral phases included quartz and K-feldspar (orthoclase). The chemical analysis further confirmed the high purity of the zeolite dust, with a substantial SiO₂ content (68.76%) and Al₂O₃ at 11.7%. Based on the experimentally determined Si/Al ratio of approximately 5.2 for the clinoptilolite dust, it is classified at the boundary between medium-silica (2–5) and high-silica (5–10) zeolites. As a result, the examined clinoptilolite dust exhibits unique combined hydrophilic and hydrophobic properties [5].

A comprehensive mineralogical and petrographic characterization of the zeolite powder from Sokyrnytsya has been previously provided by the authors [60].

Figure 6 depicts the XRD pattern of binder applied for zeolite dust agglomeration. The XRD analysis indicated that the main mineral phase was portlandite identified based on the first major peak around 18.0° and second major peak at 34 2Θ. Another mineral phase was calcite recognized based on the first major peak at 29.4° and second major peak at 48.5 2Θ. The chemical composition of the binder was as follows (in wt.%): CaO—72.93, MgO 0.41, SO₃—0.54, CO₂—1.07 and LOI—24.74.

3.1.2. Particle Size Distribution and Basic Bulk Properties

Particle size distribution (PDS) determined by laser diffraction for zeolite dust and the binder is presented in Figure 7. The obtained results showed that both materials differ significantly in terms of particle size. The powder zeolite has a grain size in the range of 0.2 to 70.0 µm, while the binder is composed of much smaller particles in range of 0.4 to 10 µm. The powder zeolite distribution and binder PDS are homogenous with a single pick located around 18 µm and 3 µm, appropriately. Both materials have a wide PDS (D90/D10 > 1), which is unfavorable.

The bulk properties of the zeolite dust and binder used for agglomeration are shown in

Table 3. Bulk properties of the natural zeolite powder (by-product) and binder for agglomeration.

Powder Type	BET [m2/g]	Specific Gravity [g/cm3]	Loos Bulk Density [g/cm3]	Tapped Bulk Density [g/cm3]	Compaction [%]	Moisture Content [%]	Avg. Grain Size [µm]
Zeolite	11.58	2.31	0.97	1.190	18.5	0.70	17.75
Binder	9.94	2.2	0.47	0.78	39.7	0.53	2,91

. The specific surface area and specific gravity of both materials are quite similar. However, zeolite has nearly twice the bulk density and proportionally lower compaction compared to the binder.

3.1.3. Structural and Textural Characterization

Figure 8 presents the SEM imaging of zeolite dust (Figure 8A) and binder (Figure 8B). The zeolite powder particles exhibited a relatively regular, sharp-edged shape (Figure 8A), while the binder appeared in rosette-like forms (Figure 8B) that strongly agglomerated with one another.

In

Table 4. Textural parameters of the natural zeolite dust for agglomeration.

Sample	SBET [m2/g]	Vtot 0.99 [cm3/g]	V BJHmes [cm3/g]	VmicBJH [cm3/g]	Vmac [cm3/g]	Average Pore Diameter 4V/A by BET [nm]	Average Pore width 4V/A by BJH [nm]
Zeolite powder	11.58	0.048	0.043	0.001	0.0041	1.01	20.11

, the detailed textural properties based on N₂ adsorption and desorption are presented. On the other hand, in Figure 9, N₂ sorption isotherms for zeolite dust before agglomeration are displayed. According to IUPAC classifications [61], N₂ sorption isotherms for zeolite powder exhibited IV-type isotherm patterns and H3-type hysteresis loops. Thommes et al. [61] indicate that the H3-type isotherm corresponds to a diverse range of slit-shaped pores with non-uniform sizes, while the IV-type isotherm is associated with capillary condensation in mesopores. These pores are present in solids composed of aggregates of plate-like particles or non-rigid agglomerates, which define the structural morphology of the studied zeolite as observed through scanning electron microscopy (SEM) (Figure 10). However, due to the intensive mechanical processing and the by-product nature of the examined zeolite, the plate-like structure is not uniformly preserved throughout the material. This can be attributed to the relatively lower specific surface area (11.58 m²/g) compared to typical high-grade zeolitic materials. The plate-like structure in zeolite is shaped by plates with thickness up to 0.100 µm (Figure 10).

The pore size distribution obtained from BJH sorption data is presented in Figure 11. The zeolite dust had a single modal of pore size, which was cantered at 60 nm, indicating the macropore structure. The average pore volume and pore diameter were 0.043 cm³/g and about 20 nm, respectively. In general, the pore network of the studied zeolite dust consisted mainly of mesopores with minimal contribution of micropores.

3.2. Characterization of Products from the Agglomeration Process

3.2.1. Basic Properties of Ribbons

Table 5. General properties of the produced ribbons.

Produced Zeolite-Based Agglomerates	Ribbon Moisture [%]	Ribbons Fragility	Ribbons Powdering
1/w/20	17.6	+	P
2/w/20	16.7	++	P
3/w/20	19.5	++++	PP
4/w/20	17.6	++++	PPP
1/w/22.5	19.4	+	P
2/w/22.5	18.9	+++	P
3/w/22.5	19.0	+++++	PP
4/w/22.5	18.2	+++++	PPP
1/w/25	22.0	+	P
2/w/25	22.9	++	P
3/w/25	23.3	++++	PP
4/w/25	23.1	++++	PPP

Ribbons fragility scale: +—very fragile, ++—fragile, +++—moderate fragile, ++++—hard; +++++—very hard. Ribbon powdering scale: P—powdering, PP—moderate powdering; PPP—no powdering.

displays the basic properties of the produced ribbons. The quality of the ribbons was evaluated based on fragility, powdering assessment, and water resistance. Due to the absence of standardized procedures for assessing the fragility and powdering of the ribbon, these parameters were determined descriptively. To facilitate the assessment, the specific scales were developed (Table 5).

The obtained test results indicated that the fragility and powdering properties of the manufactured ribbons were influenced by both the binder and water content in the materials subjected to compaction. Ribbons with the lowest binder content (2.5%) exhibited the poorest performance, with an increase in binder content resulting in more fragility-resistant ribbons. This trend remained consistent up to a binder dosage of 7.5%, after which the water content became the primary factor determining the strength of the ribbons. Regarding powdering properties, a strong correlation was observed: a higher binder content resulted in greater resistance to powdering.

3.2.2. Physico-Mechanical Properties of Produced Zeolite-Based Agglomerates

Figure 12 displays the particle size distribution of produced zeolite agglomerates through the proposed agglomeration approach. Obtained screening test results indicated that the binder content had a significantly greater impact than water content on the effectiveness of the agglomeration process. The higher the binder content, the greater the fraction yields above 0.5 mm. The highest agglomeration process efficiency (the most suitable yield of the required 0.5–2.0 grain size) was observed with the following composition of the feed for the agglomeration process: 10% binder and 25% water content (4/w/25). A very similar result (with a fraction yield above 0.5 mm only 2% lower) was achieved for the agglomerates with the composition of 7.5% binder and 22.5% water (3/w/22.5). To sum up, the highest obtained yield values were approximately 30% better than those of the agglomerate with the lowest fraction yield above 0.5 mm (fraction yield > 0.5 mm at 33%), i.e., 1/w/22.5 and 1/w/25 (fraction yield > 0.5 mm at 33%).

Table 6. Mechanical strength of the produced zeolite-based agglomerates and granular diatomite manufactured via traditional wet granulation (pan granulation with/without calcination).

Produced Zeolite-Based Agglomerates	Loose Bulk Density	Drop Strength [%]
		Granule Size [mm]
		0.5–1	1–2.5
1/w/20	881	87	84
2/w/20	860	95	93
3/w/20	853	99	98
4/w/20	824	98	98
1/w/22.5	875	88	86
2/w/22.5	850	95	93
3/w/22.5	921	98	97
4/w/22.5	854	99	98
1/w/25	879	90	88
2/w/25	865	95	95
3/w/25	877	98	98
4/w/25	850	98	98
Uncalcined granular diatomite	-	100	94
Calcined granular diatomite	-	100	100

presents the results of the gravitational drop strength test for the produced zeolite-based agglomerates with particle sizes of 0.5–1 mm and 1–2.0 mm, as well as for granular diatomite sorbents manufactured through traditional wet granulation, both before and after high-temperature calcination, for comparison. The obtained results indicated that an increase in water content had no significant effect on the crush strength of the produced zeolite agglomerates. However, it is evident that an increase in binder content enhanced the crush resistance of the agglomerates, and this trend persisted regardless of the agglomerates’ grain size. A 5% increase in binder content results in an approximately 10% improvement in drop strength. It is interesting to note that the improvement of drop resistance of produced agglomerates is observed only up to a binder content of 7.5%, beyond which no further improvement in strength occurs. Moreover, the particle size of the agglomerates had no significant impact on drop strength; however, particles with sizes of 0.5–1 mm exhibited slightly better resistance to crushing. Finally, the drop test results indicated that zeolite agglomerates manufactured via the new agglomeration approach and diatomite granules obtained through wet granulation (pan granulation with calcination) exhibited highly comparable, and in some cases nearly identical, crush strength. In this context, the agglomeration method proposed in this study appears to be a promising method for manufacturing mechanically reliable zeolite agglomerates.

3.2.3. Sorption Properties of Produced Zeolite-Based Agglomerates

• Sorption Capacity of Petrochemical Compounds—Westinghouse test

Figure 13 and Figure 14 show the results of diesel oil (VERVA ON) sorption results—determined by the Westinghouse test (Figure 15)—for produced zeolite-based agglomerates with particle sizes of 0.5–1 mm and 1–2 mm, respectively. For comparison, obtained data for diatomite sorbents produced via the traditional wet pan granulation method were also included.

According to the Polish Journal of Laws [62], sorbents approved for PPS units must demonstrate a minimum diesel oil sorption of 50% by weight. All produced zeolite-based agglomerates sized 0.5–1 mm met this requirement, outperforming the diatomite sorbents. Notably, agglomerates 4/w/22.5 and 3/w/22.5 achieved the highest sorption values—86% and 85%, respectively—exceeding those of calcined and uncalcined diatomite sorbents by approximately 54% and 45% (Figure 13). Among the produced zeolite-based agglomerates of 1–2 mm, only sample 3/w/22.5 met the 50% threshold (Figure 14).

The study indicated that binder content and particle size significantly influence oil sorption, whereas water content has a minimal effect. The produced agglomerates containing up to 7.5% binder exhibited improved sorption, while further increases in binder content showed little additional benefit. Additionally, the results showed that calcination negatively impacted diatomite sorbents, reducing sorption by approximately 15%.

For a comprehensive comparison,

Table 7. Literature-reported diesel oil sorption of mineral sorbent.

Mineral Sorbent	Diesel Oil Sorption [wt.%] (Westinghouse Test)	Reference
Clinoptilolite-type zeolite (natural zeolite dust)	50	[63]
Expanded glass	70	[63]
Commercial synthetic zeolite LTA	20	[63]
Synthetic zeolite Na-P1	91	[64]
Synthetic zeolite Na-P1	110	[63]
Synthetic zeolite Na-P1	118	[59]
Synthetic zeolite Na-P1	140	[65]
Commercial sorbent DAMSORB	83	[66]

summarizes diesel oil sorption values from the literature for other analogous mineral sorbents, measured under identical conditions using the Westinghouse test, as applied in this study. As shown in Table 7, the sorption capacities of the developed zeolite-based materials closely correlate with the properties of similar materials reported in previous scientific research. The best-performing produced zeolite-based agglomerates clearly outperformed the natural clinoptilolite powder and expanded glass, achieving significantly higher diesel oil sorption. Compared to the commercial petroleum sorbent DAMSORB, the produced agglomerates exhibited slightly better performance. Although their sorption efficiency was somewhat lower than that of synthetic Na-P1 zeolites—which can achieve values of up to 140%—this high performance is typically observed in materials developed under highly optimized and strictly controlled laboratory conditions. However, the produced zeolite-based sorbents demonstrated a sorption capacity exceeding that of the LTA zeolite by more than four times.

Figure 16 presents the used engine oil sorption results, determined by the Westinghouse method for the produced zeolite-based agglomerates demonstrating the highest diesel fuel sorption. For comparison, obtained data for diatomite sorbents produced via traditional wet pan granulation were also included.

Zeolite-based sorbents obtained through the proposed compaction method exhibited significantly higher oil sorption compared to diatomite sorbents, regardless of calcination. On average, the zeolite sorbents showed approximately 40% greater oil uptake. Among them, the 3/w/22.5 zeolite sorbent achieved 100% oil sorption, followed by 4/w/22.5 with 96%.

While the results did not clearly identify whether binder or water content—or their interaction—directly influenced used oil sorption, they did reaffirm the significant role of the agglomeration method. Moreover, these findings confirmed the advantage of the developed agglomeration technique over the traditional wet pan granulation. The novel approach enabled the production of sorbents with superior petroleum sorption capacities, likely due to the formation of secondary porosity and a less dense material structure, unlike the compact structure resulting from the wet pan method. A more detailed discussion of this issue is provided in Section 3.2.4.

Furthermore, the used oil sorption performance observed in the Westinghouse test aligns with the findings of Bandura et al. [64], indicating higher sorption for more viscous and denser oils, such as used engine oil. Higher-viscosity substances infiltrate the sorbent structure more slowly, yet penetrate more thoroughly over time [9,27,64,67,68].

• Maximum sorption capacity—droplet experiment

Maximum sorption capacity of petrochemical compounds (petrol, diesel oil, and used engine oil) was determined exclusively on produced zeolite-based agglomerates that demonstrated the highest sorption efficiency in the Westinghouse test, ensuring that only the most promising sorbents for further investigation and development were evaluated. For a broader comparison and to reinforce the findings, previously reported data on maximum sorption capacity for petrochemical compounds by zeolite materials [59] were also incorporated into the analysis (Figure 17).

The maximum sorption capacity results (Figure 17) indicated that the zeolite-based sorbent (3/w/22.5), produced via the presented new approach to agglomeration, exhibited the most versatile sorption properties, demonstrating the highest capacity for various petroleum-derived compounds: EuroSuper 95 petrol—0.4 g/1 g, Verva On diesel—0.8 g/1 g, and used engine oil—0.3 g/1 g. Moreover, this zeolite-based sorbent (3/w/22.5) outperformed diatomite sorbents produced via conventional pan granulation (with/without calcination) in its maximum sorption capacity for used engine oil and diesel, while exhibiting comparable efficiency for petrol sorption.

Given the challenges posed by the variability of oil composition and contamination in natural remediation processes, as highlighted by Sharma et al. [69], the high and consistent performance of the 3/w/22.5 zeolite-based sorbent suggests its strong potential for practical environmental applications.

Notably, while Westinghouse tests indicated the highest sorption for used engine oil, this was not fully reflected in the maximum sorption capacity tests. This discrepancy is attributed to differing test conditions—particularly exposure time. Since the Westinghouse method uses a fixed 10-min interval, maximum sorption capacity is measured until surface saturation occurs, typically within one minute. Moreover, this interpretation is supported by the findings of Muir and Bajda [59], as well as other literature data [70], which emphasize that experimental conditions during sorption measurements can significantly influence the obtained results, the adsorption kinetics, and sorption mechanism.

Surprisingly, the maximum sorption capacity of the synthetic zeolite powder Na-P1 did not exceed that of the produced zeolite agglomerates for any of the petroleum-derived compounds, and the sorption efficiency of Na-P1 was notably lower. Na-P1 exhibited petrol, diesel, and used engine oil sorption capacities of 0.5 g/1 g. In comparison, the 3/w/22.5 and 4/w/22.5 samples exhibited higher affinity for used engine oil, with capacities of 0.8 g/1 g for both.

The maximum sorption capacities of the studied zeolite dust for petroleum-derived compounds do not align with the previously reported sorption values for natural zeolite powder by Muir and Bajda [59]. In their studies [59], diesel and used engine oil removal on zeolite powder was approximately 0.4 g/1 g, and petrol sorption was around 0.3 g/1 g. This discrepancy can be attributed to the different sources of zeolite powder. While both powders are derived from Ukrainian deposits, the studied zeolite dust is a by-product of zeolite rock processing, whereas the zeolite powder used in Muir and Bajda’s study [59] was a high-quality mineral product.

• Water sorption—Westinghouse test

Figure 18 and Figure 19 present water sorption results (Westinghouse method, Figure 20) for the produced zeolite-based agglomerates, with granular diatomite sorbents received via traditional wet pan granulation for comparison. While no standardized criteria exist for water sorption, this property may be relevant in specific applications.

Zeolite sorbents with a particle size of 0.5–1 mm exhibited superior water uptake—approximately 20% higher (Figure 19) than their 1–2 mm counterparts (Figure 18)—and generally outperformed diatomite sorbent of the same size. The highest water sorption was observed in 4/w/22.5 (102%), 1/w/22.5 (100%), and 3/w/22.5 (99%) zeolite sorbents (Figure 19). However, their values remained approximately 16% lower than that of the commercial sorbent DAMSORB, (116%) [66].

It can be concluded that, with regard to water sorption, the water content used during agglomeration in the sorbent formulation plays a crucial role. Based on the conducted tests, the optimal water content ensuring the production of sorbents with the highest water sorption capacity using the proposed agglomeration method was determined to be 22.5%.

Among diatomite sorbents, the calcined sample (1–2 mm) showed the highest water sorption (approximately 89%), exceeding the best-performing zeolite sorbent (4/w/22.5) by approximately 9% (Figure 18). Interestingly, water uptake of diatomite sorbent varied inconsistently with particle size and calcination. For 0.5–1 mm granules, calcination reduced water sorption by approximately 18% (Figure 19), whereas for 1–2 mm granules, it increased it by a similar margin.

3.2.4. Textural Characteristics of Produced Zeolite-Based Agglomerates and Their Relationship with Sorption Performance

The textural parameters and pore size distribution for produced zeolite-based agglomerates, as determined by MIP, are presented in

Table 8. Textural parameters for produced zeolite-based agglomerates for petroleum sorption based on MPI.

Produced Zeolite-Based Agglomerates	Particle Fraction [mm]	Total volume of Intrusion [cm3/g]	Total Pore Surface [m2/g]	Average Pore Radius [2V/A]	Apparent Density [g/cm3]	Specific Surface Area [m2/g]
3/w/20	0.5–1	16.1056	7.8984	4.0782	1.23	18.33
3/w/25		13.5428	7.0563	3.8385	1.17	19.59
4/w/22.5		12.1479	6.788	3.579	1.31	18.72
3/w/22.5		13.1967	5.6687	4.656	1.20	16.15
3/w/22.5	1–2	11.952	6.8599	3.485	1.31	17.12

and

Table 9. Porosity and pore size distribution in the produced zeolite-based agglomerates (based on MPI).

Produced Zeolite-Based Agglomerates	Particle Fraction [mm]	Porosity	Pore Size					Mode
			1–10 nm	10–100 nm	100 nm–1 µm	1–10 µm	10–100 µm	[µm]
			Pore Content (%)
3/w/20	0.5–1	43.09	2.1	33.6	7.8	42.9	13.5	0.034
3/w/25		36.02	1.2	41.3	20.4	24.2	14.2	0.035
4/w/22.5		36.26	1.5	39.8	18.8	23.7	16.2	4.87
3/w/22.5		35.10	2.3	35.6	16.3	29.4	16.5	4.64
3/w/22.5	1–2	40.07	0.7	35.1	17.5	39.9	6.8	4.67

, respectively. The cumulative pore volume curves are shown in Figure 21 and Figure 22.

In general, the developed zeolite-based materials exhibited relatively consistent textural properties. However, slight variations were observed in specific characteristics, including total porosity, specific surface area, and pore size distribution. Total porosity ranged from 35.1% for sample 3/w/22.5 to 43.1% for sample 3/w/20, while the specific surface area varied from 16.15 m²/g (sample 3/w/22.5) to 19.59 m²/g (sample 3/w/25).

The produced agglomerates featured a predominantly macroporous structure, with macropores (>50 nm, as defined in [61]) accounting for approximately 70% of the total pore volume (Table 8). The remaining porosity was mainly mesoporous (2–50 nm, as defined in [61]), while the contribution of micropores was negligible (Table 9 and Figure 21 and 22). However, differences in pore size distribution were observed among the agglomerates. Samples 3/w/20 and 3/w/25 were primarily characterized by smaller pores (~0.035 µm), whereas samples 3/w/22.5 and 4/w/22.5 exhibited a dominance of considerably larger pores (~4.8 µm), as detailed in Table 9.

Microscopic analyses using scanning electron microscopy (SEM) and polarized light microscopy (Figure 23, Figure 24 and Figure 25) confirmed the presence of well-developed pores in the 10–100 µm range in zeolite-based sorbents 3/w/22.5 and 4/w/22.5. SEM imaging revealed that secondary porosity was shaped by varying sizes of voids. Fissures and cavities between individual zeolite powder grains and the binder resulted from the application of the novel agglomeration approach developed in this study for agglomeration of the zeolite dust (Figure 23). Moreover. SEM analysis showed that the interaction between larger zeolite dust particles appeared to promote the formation of a macroporous structure. Furthermore, the produced zeolite-based agglomerates exhibited a rough surface composed of randomly arranged particles of diverse sizes and shapes. This resulted in a heterogeneous packing pattern with booth densely and loosely compacted zones, influencing the total porosity of the agglomerates. Additionally, SEM observations showed that binder particles were embedded within the zeolite matrix, indicating good cohesion between components.

Polarized light microscopy further revealed differences in pore distribution between the sorbents. In the 3/w/22.5 sorbent, a more uniform pore distribution was observed, with a slight shift toward larger diameter pores (30–60 micrometers) compared to 4/w/22.5 sorbent (20–30 micrometers). This difference is likely associated with the higher binder content in the 3/w/22.5 sorbent, which may have influenced the structural rearrangement during agglomeration.

The relationship between the obtained textural parameters (Table 8 and Table 9, Figure 21) and the sorption properties of the produced zeolite-based agglomerates toward petroleum-derived substances (Figure 13, Figure 16 and Figure 17) was systematically evaluated. While no direct correlation was found between total porosity or specific surface area and the overall sorption performance, a more detailed analysis revealed a notable influence of pore size distribution, particularly within the 10–100 µm range.

In this context, as mentioned earlier, samples 3/w/22.5 and 4/w/22.5, distinguished by the highest proportion of pores within this range (16.5% and 16.2%, respectively; Table 9 and Figure 21), exhibited the highest sorption efficiency for diesel oil and used engine oil, as determined by both the Westinghouse and droplet test (maximum sorption capacity) methods (Figure 13, Figure 16 and Figure 17). Furthermore, the enhanced affinity of the 3/w/22.5 and 4/w/22.5 samples toward certain petroleum substances can be linked to the predominance of macropores (approximately 4.8 µm), whereas samples 3/w/20 and 3/w/25, which demonstrated lower sorption efficiency, exhibited a predominance of significantly smaller pores (approximately 0.035 µm).

The test results confirmed the previously reported correlation by Muir and Bajda [59] and Bandura et al. [64] regarding the role of mesopores in the sorption process, wherein the number and size of available pores significantly influence the sorption affinity for petroleum compounds. Conversely, analysis of the sorption properties relative to the specific surface area revealed no direct correlation. Notably, the 3/w/22.5 sample, which exhibited the highest sorption capacity for petrochemical compounds, had the lowest specific surface area (16.15 m²/g) among the produced zeolite agglomerates. In contrast, the 3/w/25 sample, despite possessing a more developed specific surface area (19.59 m²/g), displayed comparable sorption efficiencies for petrol (2 g/1 g) and used oil (2 g/1 g) and only a slightly higher sorption capacity for diesel (3 g/1 g) compared to zeolite powder, which showed consistent sorption capacities (2 g/1 g) across diesel, petrol, and used engine oil, despite having a significantly lower specific surface area (11.58 m²/g)

3.3. Interaction of Liquid Sorbate (Petroleum-Derived Compounds and Water) and Produced Zeolite-Based Agglomerates

Despite extensive research on the application of mineral sorbents (e.g., zeolites) for the removal of petrochemicals, the sorption mechanism of hydrocarbons remains a complex and challenging subject. Most studies rely predominantly on empirical models, offering limited predictive capability [71].

The complexity of the sorption mechanism of petrochemicals onto sorbents, particularly zeolites, stems from multiple factors influencing the process, including surface interactions between zeolite and sorbate (e.g., surface chemistry, charge, and composition) and textural properties (specific surface area and porosity). Based on sorption experiments, XRF analysis, BET measurements, MIP, and microscopy observations, the sorption of hydrocarbons on the produced zeolite-based agglomerates is primarily governed by physical processes occurring on the external surface, in diffusion regions, and capillaries.

The conducted research, particularly the pore size distribution analysis (see Table 9, Figure 21), and sorption data (Figure 13, Figure 16 and Figure 17) confirmed that mesopores play a key role by facilitating capillary condensation and promoting molecular diffusion within the sorbent structure. These physical characteristics enable the effective capture and transport of nonpolar hydrocarbon molecules. Ultimately, the textural parameters—particularly the meso- to macropore ratio—proved to be a determining factor in the sorption of petroleum-derived molecules (1–10 nm) within the produced zeolite-based agglomerates. These conclusions are supported by earlier studies, including the work of Carmody et al. [71], who highlighted the critical importance of sorbent textural features in oil uptake, as well as findings from other research [59,64,72]. In this context, the novel agglomeration approach proposed in this study significantly enhances hydrocarbon sorption by promoting the formation of a secondary pore system composed of both macropores and mesopores.

The selective oil/water sorption of the produced zeolite-based agglomerates is closely linked to the Si/Al ratio (5.2) in the raw material used for agglomeration. This ratio significantly reduces hydrophilicity compared to other aluminosilicate zeolites, such as mordenite, Y, A, and X zeolites. Such an adjustment enhances the affinity for nonpolar or weakly polar molecules, including certain hydrocarbons [5]. Consequently, the unique interplay between reduced hydrophilicity and increased hydrophobicity endows clinoptilolite with exceptional amphiphilic properties, enabling the efficient simultaneous sorption of both types of liquids and making it highly effective for various applications.

In addition to polarity, several other factors must be considered when interpreting selective oil/water sorption by zeolitic materials, such as the hydration state of charge-compensating cations within the zeolite framework. The presence of highly hydrated cations (e.g., Na⁺, Ca²⁺) may promote the sorption of polar molecules; however, this aspect is beyond the scope of this research.

To summarize, the sorption properties of the produced zeolite-based agglomerates are predominantly governed by surface characteristics, with hydrophobicity playing a critical role. Nevertheless, some uncertainties remain, and a more detailed, systematic investigation of the sorption mechanism will require an expanded methodological approach, including additional surface energy measurements and dynamic sorption analyses. Such studies are planned as part of ongoing efforts to develop and optimize sustainable sorbents for environmental remediation.

4. Conclusions

In conclusion, this research proposes a dual-innovation approach, combining the transformation of unmanaged natural zeolite dust—an industrial by-product—into a value-added petroleum sorbent, with the novel application of an integrated high-pressure grinding roll (HPGR) system for zeolite agglomeration. This dual-level innovation not only confirms the practical feasibility of sustainable zeolite dust valorization but also highlights significant technological advancements in agglomeration processes, offering a low-energy, environmentally friendly alternative to conventional methods.

Based on the conducted research, the following key findings were achieved:

• The proposed novel agglomeration approach enhances secondary porosity and sorption capacities of zeolite-based sorbents compared to traditional wet granulation methods.
• This agglomeration method significantly increases the specific surface area of zeolite products, representing a notable improvement over conventional techniques.
• All produced zeolite-based agglomerates (0.5–1 mm) exceeded the 50 wt.% oil sorption threshold required for petroleum spill clean-up, demonstrating superior affinity for petrochemical compounds.
• A high-performance zeolite-based sorbent (3/w/22.5) was developed, achieving maximum sorption capacities of 0.4 g/g for Euro-super 95 petrol, 0.8 g/g for Verva ON diesel, and 0.3 g/g for used engine oil.
• Formulations 3/w/22.5 and 4/w/22.5 outperformed commercial diatomite and synthetic Na-P1 zeolite in used engine oil sorption, reaching maximum sorption capacities of up to 0.8 g/g.
• The selective oil/water sorption is closely linked to the specific Si/Al ratio (5.2), which imparts unique amphiphilic properties to the zeolite-based sorbents by reducing hydrophilicity and enhancing hydrophobicity. This distinctive balance enables efficient sorption of both polar (e.g., water) and nonpolar (e.g., petroleum hydrocarbons) substances, significantly broadening the range of potential environmental applications.
• The sorption mechanism of petroleum-derived compounds onto the produced zeolite-based sorbents is primarily governed by physical processes, such as the diffusion of nonpolar organic molecules into mesopores and macropores, driven mainly by van der Waals interactions. Although sorption occurs predominantly on the external surface, the high mesopore volume, surface heterogeneity, and optimal pore size distribution facilitate capillary condensation and internal diffusion, thereby enhancing overall sorption efficiency.
• Increased binder content improves mechanical stability and sorption performance, with optimal binder levels identified at 7.5 wt.%.
• The relationship between binder and water content in zeolite agglomerates and their physical and sorption properties is complex and warrants further investigation.